Valid label keys have two segments: an optional prefix and name, separated by a slash (<code>/</code>). The name
segment is required and must be 63 characters or less, beginning and ending with an alphanumeric character
(<code>[a-z0-9A-Z]</code>) with dashes (<code>-</code>), underscores (<code>_</code>), dots (<code>.</code>), and
alphanumerics between. The prefix is optional. If specified, the prefix must be a DNS subdomain: a series of DNS
labels separated by dots (<code>.</code>), not longer than 253 characters in total, followed by a slash (<code>/</code>).

